The invention is generally directed to devices which dry air. Specifically, the invention is directed to devices which cool air to below its dew point temperature and remove the liquid which condenses at these lower temperatures, to produce dry air.
A significant need for such air drying devices is found in industrial facilities which channel compressed air to various locations in the facility. This compressed air is normally then expelled through hoses at individual stations to clean or operate machinery and the like. An important problem with such a system is that the air being compressed contains water. Due to the pressure increase and temperature variations in the system the compressed air may, on some days, be very moist and even have water droplets. This is undesirable or unacceptable in many situations.
To remove this undesirable moisture, air drying devices have, in the past, been incorporated into the compressed air lines between the compressor and the end use areas.
One type of such devices is generally known in the field as "shell and tube devices". Generally, such devices have many central tubes which contain refrigerant. A larger diameter cylinder is located around the central tubes. The air to be chill/dried is then ducted between the outer shell and the inner central tubes. This process is somewhat uneconomical, since the refrigerant is continuously regenerated.
The assignee of the present invention has for several years marketed a refrigerated air dryer which has several advantages over the "shell and tube" systems. Generally, the device has an upper portion which contains a pre-cooling section in which air entering from the compressor is partially cooled before entering the chiller located in the lower portion of the device.
Specifically, in the assignee's prior device, air enters an intake manifold which channels the air into conduit paths. The conduit paths begin in the central area of the device and spiral radially outward in parallel horizontal planes toward the exterior of the device. The effect of this upper portion is that the cooled air partially cools the air entering from the compressor. By this method, the cool air exiting from the separator is partially heated and then ducted to the exterior of the device back into the compression lines of the particular system. The heat is extracted from the incoming air by means of a heat sink material which completely surrounds each of the spiral planes. Without this heat sink material, the cool air is unable to adequately absorb heat from the incoming air.
The partially cooled air is then ducted into a series of parallel horizontal planes, each having a spiral configuration in a chiller section located in the lower portion of the device. The planes are stacked vertically with the partially cooled air traveling a spiral path from the exterior portion of the device radially inward to the interior of the device. Positioned to alternate with each of the air conduits are a series of horizontal planar spiral conduits which direct the flow of a refrigerant such as Freon. The alternating horizontal spiral planes of air and refrigerant conduits are stacked loosely in a vertical configuration. A heat sink material is dispersed throughout the chiller section of the device. The cooled air from the spiral air conduits enters a separator located in the center of the device. In the separator, condensed liquid produced from cooling the air to below its dew point temperature is funneled away leaving the cooled dry air to be ducted upward toward the pre-cooling section which was described above.
The refrigerant in the chiller section and the cooled dry air in the pre-cooling section absorb thermal energy from the heat sink material, as well as the air to be cooled. This utilization of the heat sink material means that the refrigerant does not have to be constantly regenerated. Rather, a thermostat is used to sense the temperature of the heat sink material. Thus, when the heat sink material rises to a certain temperature, the thermostat activates the compressor of the refrigeration system, and begins the cycling of the refrigerant. Conversely, when a certain lower temperature is achieved, the compressor of the refrigeration section is deactivated and the cooling of the air is achieved through the conduction of thermal energy from the air conduits directly to the heat sink material.
Although this air drier system represents a significant improvement over the "shell and tube" systems, it nevertheless possesses several disadvantages. To adequately transfer heat and cold within the system, an extremely efficient heat sink material is utilized. The heat sink material employed is usually a mixture of aluminum particles dispersed in oil. This possesses the disadvantages that the aluminum particles have a strong tendency to settle to the bottom of the device, producing a very heavy aluminum concentration in the lower portion of the device and a very low concentration of aluminum in the upper portion of the device. This results in an imbalance throughout the device in the efficiency of the heat sink material. Secondly, the aluminum and oil heat sink material is extremely difficult to manage and creates significant clean-up problems if leaks occur. The aluminum and oil heat sink material is also quite expensive.
In view of the above problems, a significant need exists for improved air drier devices.